Brake boosters of this type are widely used and known. The booster housing of a brake booster of said type normally has at least two thin-walled housing shells which are connected to one another or fixed or coupled to one another. Here, in the booster housing, at least one negative-pressure chamber is pneumatically separated from a working chamber by a diaphragm composed of elastomer material. Here, the diaphragm lies in regions on a rigid diaphragm plate, which, during operation, is axially movable over a structurally defined stroke range.
To compensate for the axial movement, the diaphragm has a rolling fold, which is arranged radially at the outside, between the diaphragm plate and the inner wall of the booster housing and which, during operation, rolls on a rolling region on the inner wall of the booster housing.
The projected area of support of the diaphragm on the diaphragm plate functions as a pneumatically effective area for the build-up of the boost force and significantly influences the efficiency of the brake booster. It is therefore sought to minimize the radial spacing between the diaphragm plate and the booster housing over the entire stroke range, and therefore, the booster housing of the known pneumatic brake booster is, in the rolling region, cylindrical or formed with a minimal, production-related demolding taper, usually in a range between 1° to 2°.
Brake boosters with different stroke ranges are required for different vehicle applications. For the purpose of cost savings, it is sought to realize this on the basis of a modular system by virtue of only a few components having to be changed or exchanged, for example an axially deeper housing shell for a larger stroke range and vice versa. In this method, in the case of the known brake boosters, the diaphragm must also be changed or provided in several versions.
For example, the rolling fold of a diaphragm designed for a long-stroke brake booster would form a large bladder in the case of small-stroke brake boosters even at the maximum strokes thereof, thereby unfavorably reducing the volume of the vacuum chamber and increasing that of the working chamber. However, this reduces the efficiency and the magnitude of the achievable boost force, and degrades the response behavior.
In the case of a diaphragm designed for a small-stroke brake booster being used in long-stroke brake boosters, the diaphragm would, at maximum stroke, no longer lie fully against the diaphragm plate, lift off from the latter, thereby reduce the pneumatically effective area, and consequently likewise reduce the efficiency and the magnitude of the achievable boost force.